The Pi-hole team does neither develop nor endorse apps for Umbrel's app store, and Umbrel OS isn't on Pi-hole's list of supported OSs .
So far, we've only received reports for failing attempts on Umbrel, see e.g. Pi-Hole in the Getumbrel node does not install, it always stays on or DNS resolution is currently unavailable - Umbrel.
If Umbrel's app isn't working for you, consider to file an issue with Umbrel's support.